In bicycles provided with a speed gear having a spring-loaded derailleur, in particular in sports and racing bicycles, the drive chain is caused to pass from one sprocket to another of the free wheel by the lever of a gear selector operated by the cyclist, and which by means of a cable shifts the gear derailleur so as to align it with that sprocket of the free wheel corresponding to the desired ratio.
This operation is carried out by feel, as it is not possible for the cyclist to observe what happens behind him.
On numerous occasions, and in particular during cycle races, the proper execution of a gear change can be compromised by the state of mind of the competitor, the gear change either being made onto sprockets other than those intended, or requiring a lengthy time which is completely unacceptable.
In order to make the aforesaid operation easy and reliable to execute by the cyclist within reasonable time, speed gear selectors have already been provided in which the lever operable by the cyclist and mounted rotatable against friction on a pivot is associated with a snap-action mechanism controlling a plurality of different positions of the lever, with which a like number of positions of correct alignment of the speed gear with the various sprockets of the free wheel correspond.
Means for activating and deactivating said snap-action mechanism on command have also been associated with the gear selector operating lever and with the snap-action mechanism itself. This leaves the cyclist free at every moment to choose between operation by feel and operation by preselecting the speed gear ratios.
In these gear selectors there are generally provided a main friction device which opposes the return spring of the speed gear and a secondary friction device which opposes the operation of the means for activating and deactivating the snap-action mechanism.
The methods of the known art used for obviating the aforesaid problems have up to the present time comprised a very complicated mechanism requiring a large number of component parts, the assembly and disassembly of which are neither easy nor immediate. Moreover, these known methods do not allow ready adaptation to the various types of free wheels existing on the market, nor to the different and numerous combinations of sprockets which can be used in them by cyclists during races. It therefore happens that even today replacing one free wheel by another (for example replacing a wide free wheel comprising six sprockets by a narrow free wheel comprising seven or eight sprockets, this being a frequent operation in sporting activity and often done during an actual race or races which take place overy very short times) requires work to be carried out which not only involves the gear selector but is also too long and complicated, and therefore in practice impossible to do during a race and/or within a short time. This has up to the present time hindered the application and marketing of improved gear selectors of the aforesaid type, or has limited their use by cyclists, with obvious disadvantages.
The object of the present invention is therefore to decisively improve the characteristics of these devices, this object being attained by a gear selector of extremely simple, compact and effective structure, which with optimum operation efficiency allows virtually immediate adaptation to any type of free wheel and to any number and combination of sprockets in free wheels produced by any manufacturer. The bicycle gear change can therefore be easily implemented by the cyclist, either by choosing preselection operated by snap-action, or by choosing the method based on feel and excluding this preselection.